The worst (best) part was Dr Heiter, played by Dieter Laser. He was truly creepy looking, and his acting made you feel like perhaps he was this scary in reality too. The film was about his being a surgeon; he used to separate conjoined twins, but then becomes fixated with joining living things.
Naturally, this leads to his ideal of a human centipede, connected by sewing their mouths to each others butts, so that they share one digestive track. Implausible in the long-term, and hilarious, so I was glad when one of the three victims died from infection. That was the most medically accurate part.
The film was not scary, but hilarious. I just couldn’t stop laughing at what idiots the characters are. One of the two female leads had the chance to escape, but hides instead of smashing the window to escape straight away. And the Japanese guy, played by Akihiro Kitamura, who is also a captive, actually stabs Dr Heiter with a scalpel, but only in the foot and leg. He goes crazy and bites him, but instead of using his chance to kill the crazy Doctor, or knock him unconscious at least, he chooses to just attempt to run away (difficult with two girls surgically attached).
I had no real sympathy for the characters because their survival instincts were poor, I like it when characters truly try their best and are beaten down, but these three were mainly moronic and therefore deserved it. The very few chances they had to escape they wasted completely.
As ridiculous as this film was, it’s worth watching because it’s one of the funniest films I’ve seen in a long time, and wasn’t too badly shot.